According to the United States Humane Society, there are approximately 78 million dogs and 86 million cats in the United States. The American Pet Products Manufacturers' Association (APPMA) estimates that 62% of United States households provide a home for a pet, compared with 56% in 1998. The APPMA reported that Americans spent over $13 billion on veterinary care, with the average lifetime cost of care for either a medium-size dog or cat being approximately $10,500. Globally, the growth of the pharmaceutical market for companion animals is comparable to that of human healthcare.
About six million dogs are diagnosed with cancer each year in the United States. Incidence of all cancers was 99.3 per 100,000 dog-years in male dogs and 272.1 in female dogs, due to the high rate of mammary cancer observed in female dogs (bitches). The highest incidence rates were detected for mammary cancer (IR=191.8) and for non-Hodgkin's lymphoma (IR=22.9) in bitches and for non-Hodgkin's lymphoma (IR=19.9) and skin cancer (IR=19.1) in male dogs. Cancer incidence in dogs increases dramatically with age increasing for bitches from 23.7 to 763.2 and for male dogs from 16.5 to 237.6 in animals aged < or =3 years and >9-11 years, respectively.
Incidence rates of cancer in cats are reported as 155.8 per 100,000 animals. The highest incidence rates in cats were detected for lymphoid tumors (IR=48.1) and skin cancer (IR=34.7). With significant incidence also reported for breast (IR=25.4); connective tissue (IR=17.0); mouth and pharynx (IR=11.6); digestive tract (IR=11.2); respiratory (IR=5.0) and bone (IR=4.9).
Cancer, of course, can occur in other species. Several years ago, a top-class thoroughbred race horse was diagnosed with lymphoma; the horse was retired from racing but died during its four-year-old season, an extremely young age for a horse. Such fatalities represent significant economic loss to the owners of such animals.
Similar to humans, cancer is the leading cause of death among older cats and dogs, and accounts for about 50% of deaths each year. Pain is common in pets with cancer, with some tumors causing more pain than others. The issue of pain in cancer in animals is difficult to evaluate, because there is no definite way of evaluating the extent of pain and the resulting discomfort experienced by the animal. However, as in humans, pain is related to the size and location of the cancer and the involvement of nerves; cancer in or associated with organs that have a higher degree of innervation tends to produce a higher degree of pain. In addition to the actual malignancies, pets can experience pain associated with cancer treatments, such as surgery, radiation therapy, or chemotherapy. Untreated pain decreases the pet's quality of life and also can prolong recovery from the illness or treatment; it can also affect the owner emotionally.
Cancer cachexia (a term referring to progressive severe weight loss) is frequently observed in pets with cancer. Pets with cancer lose weight for a number of reasons: one of those reasons is lack of appetite, and another of those reasons is cancer-induced altered metabolism. Some of the causes for decreased appetite are related to the cancer itself (for example, tumors may physically interfere with food chewing, swallowing, and digestion processes, depending on their size and location) and some may be related to the side effects of cancer treatment (for example, some chemotherapy drugs cause nausea and vomiting, and radiation therapy can cause mouth inflammation).
Strategies for treatment of cancer in pets, such as cats and dogs, are generally similar to strategies employed for treatment of cancer in humans. In general, the basic strategies are one or more of surgery, radiation, and chemotherapy. Many of the chemotherapeutic approaches employed for treatment of cancer in humans have been employed or evaluated in pets, such as the use of monoclonal antibodies, targeted therapy, cancer vaccines, the simultaneous use of multiple therapeutic agents, and other approaches.
Therefore, there is a definite need for improved veterinary treatment of cancer. There is a particular need for agents that can be administered to treat a wide variety of malignancies and that are well tolerated without causing significant side effects.